FR2682995A1 - DEVICE FOR CONTROLLING THE OPENING AND CLOSING OF THE DISCHARGE VALVES OF A TURBOJET ENGINE. - Google Patents

Abstract

The control device according to the invention makes it possible to quickly position the discharge valves (1) of an airplane turbojet in a wide open position when it is at low speed to avoid extinction. The principle consists in temporarily interrupting the action of a control return cable (10), when the valves are opened from a certain determined value. The device consists of a drive tab (22) integral with an already existing crank, to drive the translation of the return cable (10) when the latter is not blocked by a translation stop (23) . Application to the opening of the discharge valves of bypass turbojets.

Description

DEVICE FOR CONTROLLING OPENING AND CLOSURE

  DISCHARGE VALVES OF A TURBOJET ENGINE

DESCRIPTION

TECHNICAL AREA

  The present invention relates to turbomachines and more particularly to twin-jet aircraft turbojets that are equipped with

discharge valves.

PRIOR ART AND PROBLEMS POSED

  With reference to FIG. 1, in a conventional manner, such turbojet engines comprise upstream in the primary flow, that is to say in the internal channel 2, a low-pressure axial compressor 3 supplying compressed air to a chamber combustion system 8 in which the air is mixed with pressurized fuel This mixture is burned to give downstream of the chamber 8 of the energy to an axial turbine which drives the high pressure compressor 4 and whose output gas provide the thrust useful for the propulsion of the aircraft Such turbojets have a totally axial configuration They absorb through their front inlet not only the air necessary for their operation, but also, depending on the climatological conditions, sand, water, these elements that are rather a hindrance to the

operation of the turbojet engine.

  This is particularly the case when the aircraft encounters a storm or crosses a dense cloud and

  large volume such as a cumulus or cumulo-numbus.

  Large amounts of water in the form of rain

  or hail then enter the compressor.

  If the engine is in full throttle, the water is vaporized immediately If it penetrates to the combustion chamber it is there in the state

  sufficiently hot steam and is sprayed.

  It does not cause the extinction of the combustion chamber which is then fed by a high flow of fuel On the other hand, this is not the case when the aircraft is downhill, for example during an approach phase before landing In fact, in this case the turbojet engine is idling, resulting in a compression ratio and a low fuel flow If a large water flow or pieces of ice then reach the combustion chamber, they can cause the extinguishing of the burners It is added that the spark plugs, when they are wet, are

  inoperative when engine shutdown occurs.

  If the pilot is not able to leave the area of critical rain, the engine (s) can then be totally stopped, with the risks that this entails. This is the common mode of extraction of

all engines.

  In order to avoid such troubles, which can be catastrophic, it is possible to eliminate the water which entered the combustion chamber in order to avoid extinction. For this purpose, discharge valves 1 are used which open the door. internal channel 2 on the external channel 6 These valves are placed between the upstream compressor 3 and the rear compressor 4 As shown by the arrow referenced 5, part of the flow into the upstream compressor 3 is diverted to the outer channel 6 As a result, the mass of water or ice likely to seriously disturb the operation of the turbojet engine is deflected. These discharge valves 1 are originally intended to prevent the phenomenon of "pumping" of the low pressure compressor 3, when it is forced to pass a flow rate higher than that Lui that can accept the high pressure compressor 4 , located downstream. With reference to FIG. 2, the usual operation of the discharge valves follows the curve represented in strong lines on this figure. On the abscissa the engine speed is plotted, the ordinate is plotted the opening of the valves As can be seen by the curve in FIG. strong line, when starting the engine, the valves are in almost open position The closing law of the valves follows the curve which decreases in a relatively regular manner, while making a bearing just before the point marked C The curve tangent the line of closing the valves to the point

  D which corresponds to a regime of full gas.

  This operation is implemented on the discharge valves by control means and pre-programmed hydromechanical control means for controlling the opening and the

  closing the valves according to this determined curve.

  The object of the invention is to modify the operating law of the opening and closing of the valves without changing the equipment already existing on the turbojet engines, in particular with regard to the control of these discharge valves This modification of the law will allow a longer and more consistent opening of the discharge valves as long as the engine has not reached a predetermined sufficient speed This theoretical change is shown in Figure 2 by the dashed line curve from point A to point D via

  B and C When operating at increasing speed.

  Conversely, the very purpose of the patent is to make that on reduction of speed under conditions of high humidity, the discharge valves pass very quickly from point C to point B to avoid any

risk of extinction of the reactor.

SUMMARY OF THE INVENTION

  The main object of the invention is, for this purpose, a device for controlling the opening and closing of the discharge valves in a turbojet engine. The flow, by motor means, of the control means and a system. regulator for actuating the valves according to a determined operating curve, and comprising a Levers return connected on the one hand to a valve and on the other hand to a return cable connected Himself to the system

  regulating the control means.

  According to the invention, there are provided means for suppressing the action of the return cable, as long as the valves have an opening greater than a determined value, so that the control means do not actuate these valves according to said curve, as long as 'they are open above the value

determined.

  In a main embodiment of the invention, the return cable is secured to a lever for controlling the return cable and on which is in temporary support a drive lug whose movement vis-à-vis the lever is proportional to the opening and

closing the valves.

  In this case, the lever return comprises beforehand a bead wire fixed on the one hand to the valve and on the other hand to the end of a crank pivotally mounted about an axis of rotation, this crank is integral in rotation the drive lug that pivots around the axis to describe a circular arc and drive the return cable by leaning

on the lever.

  Preferably, the lever is mounted free to rotate about the axis and the head is mounted free to rotate in a hinge of the end

return cable.

  To complete this device, since the return cable is constantly subjected to a restoring force, the lever may be equipped with a hook whose end bears against a cable stop, adjustable in translation and whose position determines said determined value of opening of the valves, which allows a setting of the opening of the

low speed valves.

LIST OF FIGURES

  The invention and its technical characteristics will be better understood when reading

  the following description, accompanied by several

  FIGS. 1 and 4, respectively, showing the location of the discharge valves in a turbofan engine; Figure 2, the two operating laws of the discharge valves according to the prior art and according to the invention; Figure 3, the device according to the invention with respect to the opening of a discharge valve; Figure 4, the device according to the invention in detail; FIGS. 5A, 5B and 5C, three positions of

  operation of the device according to the invention.

  DETAILED DESCRIPTION OF AN ACHIEVEMENT

OF THE INVENTION

  During the start of the turbojet, up to an operating point of the latter which can be adjustable, the opening of the valves is maximum This corresponds to the horizontal segment AB of the curve of Figure 2 The points B and C have a corresponding abscissa at the operating point of the turbojet engine from which the opening of the valves can be decided. This adjustable operating point can be, for example, 40% of the maximum rotational speed of the low-pressure body of the turbojet engine.

to be chosen.

  The second vertical segment BC of this curve thus symbolizes the beginning of the closure of the valves while the engine is running at a constant speed. The point C symbolizes an opening of the valves which is the same as for the traditional closing law and for the same point determined from this point C, the valves can

  resume the closing cycle of the old law.

  This last part is symbolized by the C-D part of the common mixed curve with the curve representing the traditional closing law according to

the prior art.

  It is understood that, during the passage of dense clouds or hail by the aircraft, an additional amount of water will be released to the secondary flow, if the turbojet engine speed is below the regime symbolized by points B and C This amount Additional water discharge corresponds to the area of the surface between the curve of the prior art and the three points A, B, and C. The extinction margin of the combustion chamber is increased. FIG. 3 represents, on the one hand, at the bottom of the figure, a discharge valve 1, as described in FIG. 1, and at the top of FIG.

  the control device according to the invention.

  The discharge valve 1 has been shown open, so as to let a certain portion 5 of the flow from the primary channel 2 to the secondary channel 3 The control means 30 are connected to the control device by a strong and mixed line symbolizing a rod 14 whose two ends are shown These control means drive an actuating device 7 of the discharge valve 1 via motor means 40 The movements of the actuating device 7 of the valve simultaneously cause the displacement horizontal translation of the rod 14 This causes in known manner a crank 15, 18 in rotation about an axis 20 The second portion 18 of the crank is connected by a hinge at the end of a return cable 10 Ce the latter is connected to the control means of the control system of the discharge valves 1 Its role is to signal the actual open position of the discharge valves 1 En Indeed, it is controlled by a portion of a discharge valve 1 via the rod 14 It is therefore an element of the servo control loop of the control valves

discharge 1.

  The control device according to the invention consists mainly of a return of levers comprising parts involved in the transmission of this return movement between the rod 14 and the return cable 10 The principle consists in interrupting the translational movement 10 as long as the valves are open, that is to say in the area corresponding to the path A to C of the curve of Figure 2 It is therefore to immobilize the return cable 10 A Indeed, the main elements of the embodiment described are constituted by a drive lug 22 secured to the crank 15, 18, a lever 19 integral with the head of the return cable 10 and a cable stop 17 immobilizing the return cable during the period of wide opening of the discharge valves 1 The operation of the device will be described in detail with reference to FIG. 4 Nevertheless, it can be summarized by indicating that the return cable 10 is immiscible. in translation by the cable stop 17 regardless of the position of the crank 15, 18 at the beginning of the opening, as long as the drive lug 22 is not in contact

  with the lever 19 secured to the return cable 10.

  Subsequently, the rotation of the crank 15, 18

drives the cable in translation.

  With reference to FIG. 4, the full open position of the valves corresponding to the points A and B of the curve of FIG. 2 is indicated by the same letters A and B. The rod 14 is tilted to the right. The crank consists of a first lever 15 and a second control lever 18, integral with each other about an axis of rotation, is oriented downwards, the end of the lever being pulled by the rod 14 In this position, it is found that the second lever 18 is not in rotational contact with the lever 19 secured to the return cable 10 This lever 19 is in fact, in the embodiment described here, mounted freely in rotation around the horizontal axis 20 and around the head In fact, the latter is held at a sufficient height by an adjustable cable stop 23 which is fixed relative to the entire device and which maintains the lever 19 at a height determined by means of 'a hook 21 solidai The hook 21 is indeed at its end bear against the abutment 23 The return cable 10 is thus maintained at a desired height This means that as long as the crank 15, 18 has not taken an angular orientation to the left sufficient to rotate the lever 19 by its drive support 22, the return cable is immobilized in the defined position

by the cable stop 23.

  As shown in FIGS. 5A and 5B, when it is a question of starting the closing of the discharge valves, that is to say of proceeding to a phase corresponding to the segments B, C of FIG.

  rod 14 pushes the lever 15 of the crank.

  The orientation of the latter changes until the moment when the driving lug 22 integral with the second lever 18 comes into contact with the lever 19. It is then at point C of FIG. 2. FIG. 5A corresponds to the position of valve open and Figure B corresponds to said switching point C. From this moment, and with reference to FIGS. 5B and 5C, the closure of the valves leads the rod 14 to continue its translation to the left as indicated by the arrow and to rotate the lever 19 around the axis 20 The hook 21 which is secured to it off the abutment 23

  and the return cable is driven up.

  This operation corresponds to the last segment C, D of FIG. 2 and the return cable 10 has the same function as in the case of the prior art. FIG. C corresponds to the closed valve position or the point

D of Figure 2.

  It can thus be seen that it is possible to modify the servo-control system already existing in the prior art (the rod 14, the crank, 18 and the return cable 10) by simply adding a few modifications. They consist of the addition of the drive support 22 of the lever 19

  and its hook 21 and the cable stop 23.

  It is also advantageous to be able to adjust the point C of FIG. 2 from which, when closing the discharge valves, the return cable 10 resumes its initial role. This adjustment can be obtained by making the position of the stop adjustable. For this purpose, it is fixed to a support 17 which is slidably mounted along a frame of the turbojet engine 27 and whose position

  is adjustable by means of a setting screw 25.

  Of course, the shape and arrangement of the various elements described in this figure and cooperating with the fact that the action of the return cable is interrupted when the valves are in the open position, are only an example of embodiment The inventive concept of the The invention resides in immobilizing the return cable 10 in a given position, when the discharge valves are in the open position. The embodiment described by this FIG. 4 is only an exemplary embodiment adapted to certain existing turbojets. and using a servo loop implemented by a

  rod 14 and a return cable 10.

  The main advantage sought and obtained with the control device according to the invention is to improve the operating conditions of the engine in a humid atmosphere (crossing heavy thunderstorms, hail, snow) and especially to avoid the extinctions of the chamber. combustion that lead

stopping the engine.

Claims (4)

  1 Control device for opening and closing of discharge valves (1) in a turbofan engine by means (40) and control and regulating means (30) for actuating the valves (1) according to a given curve, comprising a lever return connected on the one hand to a valve (1) and on the other hand to a return cable (10) itself connected to the control and regulating means (30), characterized in that it comprises means for suppressing the action of the return cable (10), as long as the valves (1) have an opening greater than a predetermined value, so that the control and regulating means (30) do not actuate the valves (1) according to said determined curve as long as the valves (1) are open above said value.   2 Device according to claim 1, characterized in that, in the lever return, the return cable (10) is secured to a Lever (19) for controlling the return cable (10) and on which is in temporary support a drive lug (22) whose displacement relative to the lever (19) is proportional to the opening and closing movements of the valves (1), a cable stop (23) being provided to prevent the cable back (10) to be constantly resting on the paw drive (22).   3 Device according to claim 2, wherein the lever return further comprises a rod (14) fixed on the one hand to the valve (1) and on the other hand to the end of a crank (15, 18). , rotatably mounted about an axis (20), characterized in that the drive lug (22) is integral in rotation with the crank (15, 18) which pivots about the axis (20) and describes an arc of circle and drives the return cable (10) relying on the lever (19).   4 Device according to claim 3, characterized in that the lever (19) is rotatably mounted about the axis (20) and whose head is rotatably mounted in a joint   (26) of the end of the return cable (10).   Device according to any one of   Claims 2 to 4, the return cable (10) being   constantly subjected to a return force, characterized in that the lever is equipped with a hook whose end bears against a cable stop (23) adjustable in translation so that its position   determines said determined value.